Q&A: Soil Gas Standards

Q: How is soil gas regulated in Texas?

A: Soil gas is treated differently in Texas than in many other states. It is not routinely sampled; in fact, the Texas Commission on Environmental Quality (TCEQ) has not established indoor air standards. While TCEQ has established risk-based exposure limits for some volatile organic carbons in the air, those limits only apply to outdoor air. The U.S. Environmental Protection Agency’s (EPA) Vapor Intrusion Screening Levels (VISL) are the default for evaluating indoor air or sub-slab soil gas concentrations.

Currently, internal working groups at TCEQ are developing guidance for soil gas sampling and appropriate protective concentration levels (PCLs). In the meantime, soil and groundwater are the main focus of most site investigations and used as indicators for vapor issues.

TCEQ assesses the risk of exposure to vapor by evaluating the concentrations of chemicals of concern (COCs) in groundwater and subsurface soil (greater than 15 feet below ground surface for residential and five feet below ground surface for commercial/industrial). Soil and groundwater concentrations are then compared to a PCL developed for the inhalation of volatile COCs from soil (^AirSoil_Inh-V) or groundwater (^AirGW_Inh-V). The inhalation of gas and particulates in surface soils is evaluated as part of the PCL covering exposure via ingestion, dermal contact, inhalation of volatiles and particulates, and ingestion of vegetables in contact with COCs in soil (^TotSoil_Comb); however it is not evaluated separately.

In rare cases, depending on the regulatory program (e.g., Voluntary Cleanup Program, Corrective Action, Petroleum Storage Tank) and the type of site being investigated, TCEQ may request sampling of soil gas or indoor air concentrations when ^TotSoil_Comb, ^AirSoil_Inh-V, or ^AirGW_Inh-V PCLs are exceeded. In those cases, it’s best to closely coordinate with TCEQ.

In Texas, Langan currently conducts soil vapor sampling to evaluate exposure risks for national clients using EPA methods and VISL for comparison. Once TCEQ issues its guidance, Langan will be prepared to help the regulated community assess soil vapor.

About Kate McCarthy, PG
Kate McCarthy is a Senior Project Manager in Langan’s Austin, Texas office. She is a professional geologist with nearly 25 years of experience performing environmental site investigations, environmental due diligence (Phase I and Phase II), preparing regulatory compliance reports for the Texas Commission on Environmental Quality (TCEQ) Petroleum Storage Tank (PST) Program, Texas Risk Reduction Program (TRRP), and Resource Conservation and Recovery Act (RCRA) permits.

In 2019, McCarthy was Union Pacific Railroad 2019 Site Remediation Project Manager of the Year Nominee. In 2020, she was Golder’s 2020 CEO Sustainability Award Finalist in the category of Community Impact.